Piston accumulator and system using the same for use with high pressure hydraulic apparatus

ABSTRACT

A piston accumulator for hydraulic actuators, presses or the like is formed with a plunger piston for reciprocating within gas and liquid receiving chambers which are sealed and separated from each other in such an effective manner that compressed air rather than nitrogen may be used in the gas chamber without the danger of &#39;&#39;&#39;&#39;dieselization.&#39;&#39;&#39;&#39; The plunger piston is guided and sealed by a piston and guiding means intermediate the liquid and gas chamber rather than by usual cylinder bore walls. The expense of machining such internal cylinder bore walls is eliminated as well as the problem of leakage caused by scoring and scratching such machined cylinder bore walls by spacing the chamber walls from the piston plunger wall and using a soft bearing material for the piston sealing and guiding means into which dirt or other material may embed. Means are provided for varying pressure and/or volume of gas to achieve various operating characteristics for the hydraulic press.

United States Patent Chanin [72] Inventor: Milton Chanin, 2 Fern Lane,

Matawan, NJ. 07747 [22] Filed: Dec. 12, 1969 [21] Appl. No.: 884,674

[52] US. Cl. ..60/51, 91/394, 91/404, 92/165, 138/31, 277/2 [51] Int. Cl. ..FlSb 1/04 [58] Field of Search ..91/394-396, 404; 92/86, 165; 138/31, 106; 277/2; 60/51 [56] References Cited UNITED STATES PATENTS 2,982,100 5/1961 Sinclair ..60/51 3,100,965 8/ 1963 Blackburn ..60/51 3,375,658 4/1968 Slover ..60/51 1,220,343 3/1917 Kimball ..138/106 X 2,592,613 4/1952 Snyder ..138/31 2,708,949 5/ 1955 Krapf ..138/31 2,746,485 5/1956 Ashton 138/31 2,778,342 l/l957 Ringman ....91/404 2,817,361 12/1957 Mercier ....138/31 2,911,952 11/1959 Peras ..91/394 X 3,392,983 7/1968 l-lajner .277/2 X [151 3,681,918 [451 Aug.8, 1972 FOREIGN PATENTS OR APPLICATIONS 1,071,528 12/1959 Germany ..92/165 944,5 14 12/ 1963 Great Britain ..138/31 OTHER PUBLICATIONS German Printed Application 1,071,528 Gopfert; 12- 1959 Primary Examiner-Edward J. Earls Attorney-Fitch, Even, Tabin & Luedeka [57] ABSTRACT A piston accumulator for hydraulic actuators, presses or the like is formed with a plunger piston for reciprocating within gas and liquid receiving chambers which are sealed and separated from each other in such an effective manner that compressed air rather than nitrogen may be used in the gas chamber without the danger of dieselization. The plunger piston is guided and sealed by a piston and guiding means intermediate the liquid and gas chamber rather than by usual cylinder bore walls. The expense of machining such internal cylinder bore walls is eliminated as well as the problem of leakage caused by scoring and scratching such machined cylinder bore walls by spacing the chamber walls from the piston plunger wall and using a soft bearing material for the piston sealing and guiding means into which dirt or other material may embed. Means are provided for varying pressure and/or volume of gas to achieve various operating characteristics for the hydraulic press.

1 1 Claims, 6 Drawing Figures PATENTEDAus a 1912 ATTYS,

PISTON ACCUMULATOR AND SYSTEM USING THE SAME FOR USE WITH HIGH PRESSURE HYDRAULIC APPARATUS This invention relates to a piston accurnululator for use with hydraulic apparatus and more particularly to piston accumulators used with high pressure actuators, presses or the like.

The present invention is described hereinafter in connection with apparatus such as a hydraulic press wherein high pressure fluid actuates a piston or ram for purposes such as punching, forging, forming, impact extruding, etc. In a typical installation, an accumulator for such apparatus includes an elongated, machined internal cylindrical bore within which the piston is guided for reciprocating travel. One side of the piston is exposed to nitrogen gas typically, at 2,000 psi. or upwards thereof, which is charged from a nitrogen tank or storage bottles. A hydraulic fluid such as oil is disposed on the other side of the piston for transfer from the accumulator cylinder to a cylinder in which the ram is disposed. Heretofore, it has not been possible to use compressed air rather than nitrogen as there is a danger of dieselization or explosions if air should leak past the piston seal or packing and combine with the oil. However, the use of nitrogen or some other inert gas at high pressure is disadvantageous as the nitrogen tank or bottles are bulky and must be returned with considerable nitrogen gas within them when the pressure within the tank or bottles is reduced below or about operating pressure.

Known piston accumulators also are costly to manufacture as they generally require an accumulator cylinder having a long, internal cylindrical bore which is difficult and expensive to machine to close tolerance dimensions to assure a tight seal with the piston. Such long internal bores are also susceptible to scratching by foreign matter such as, for example, pipe scale, metal shavings, dust or dirt which becomes lodged between the movable piston wall and the cylinder wall. Scratches allow the escape of nitrogen past the cylinder. Moreover, such long internal bores are difficult to harden or chrome plate to reduce their tendency to scratch and, if hardened are difficult to grind, machine or otherwise surface to close tolerance dimensrons.

Accordingly, an object is to provide a low cost, as compared to the prior art, piston accumulator of the foregoing kind.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a longitudinal view of an accumulator embodying the novel features of the invention and of a system in which the accumulator may be employed;

FIG. 2 is a longitudinal, broken cross, sectional view of the accumulator of FIG. 1;

FIG. 3 is an enlarged cross sectional view of a piston sealing and guiding means constructed in accordance with the preferred embodiment of the invention;

FIG. 4 is an enlarged, fragmentary view of support shoes for a horizontally disposed piston plunger;

FIG. 5 is an enlarged fragmentary view of engageable surfaces on an end plug and the piston plunger; and

FIG. 6 is a graph diagrammatically illustrating pressure-volume curves for various pressure and volume.

relationships.

As shown in the drawings for purposes of illustration, the invention is embodied in a piston accumulator 1 l of the kind suitable for use with various kinds of hydraulic apparatus such as, for example, a hydraulic press or a high energy impact machine 13 having a press cylinder 14 in which is an actuator ram 15 which may be exposed to a predetermined, hydraulic pressure from a line 21 extending to a housing 22 for the accumulator in which is a hollow chamber 23 having a hydraulic liquid such as oil therein. Oil in the oil chamber 23 is under pressure from a piston plunger 25 which extends into a gas cylinder 29 in which is an intemal gas chamber 31 having high pressure gas therein. In accordance with the preferred embodiment of the invention, compressed air may be used in the gas chamber rather than nitrogen; and the expensive to grind or machine long internal cylinder bore having close tolerance dimensions is eliminated and standard, inexpensive stock tubing may be used to construct an accumulator housing comprised of the oil and gas cylinders. In lieu of the conventional long cylinder bore for guiding and sealing with the piston, an accurate guiding of the piston plunger and the seal between the respective oil and gas chambers 23 and 31 is achieved by use of a piston guide and sealing means 33 in the form of a short bushing or sleeve 35 which preferably has a bearing surface means 37 having a slidable close tolerance fit with a long exterior wall 39 of the tubular shaped piston plunger 25. An exterior, outer diameter wall such as that of the piston wall 39 may be readily hardened and subsequently ground, machined or surfaced to close tolerances for sliding within and along the bearing surface means 37. Preferably, the bearing surface means 37 is formed with a soft bearing material such as bronze or babbit into which foreign matter may embed without scratching long grooves which would allow gas to flow therethrough from the gas cylinder 29. Should compressed air be used in the gas cylinder to drive the piston plunger 25, the piston sealing and guiding means is formed with an air bleed means in the form of an annular groove 41 separating an air seal portion 43 (FIG. 3) of the sealing surface means from an oil seal portion 45 of the sealing surface. An air bleed line 47 and a port 49 are connected in fluid communication with the annular groove 41 to discharge any air, should air leak past the air seal portion 43 and into the annular groove.

Referring now in greater detail to the individual components of the invention, the gas cylinder 29 of the accumulator housing 22 may be formed from a stock steel tube with its interior bore defining wall 51 unmachined,

. unground and unhardened as its bore defining wall 51 does not engage the piston plunger 25 and is separated therefrom by an annular space 52. An end cap or plate 53 is secured as by welding one end of cylinder tube to seal one end of the gas chamber 31. A gas inlet port 55 is formed by a machined bore in the end cap 53 to admit compressed gas, such as, for example, compressed air at 2,000 psi into the gas chamber 31. Preferably, the gas inlet port 55 opens at the longitudinal axis of the gas cylinder 29 and into a hollow interior 57 in the piston plunger 25 to purge any accumulated water during an air bleeding operation and to provide a more favorable gas volume balance between a working or unseated position for the piston in which the piston is spaced from a circular groove seat 59 in the end cap and a non-working or seated position in which an end 61 of the piston plunger is seated in the seat 59, as will be explained in greater detail.

In a similar manner the oil cylinder 24 may also be made with a standard stock tubular shaped cylinder of circular cross section without grinding, machining or surface hardening its internal bore wall 64 which has a larger diameter than the outer diameter wall 39 of the piston plunger 25 and is spaced therefrom by an annular space. The port for the oil conduit 21 may be anywhere along the cylinder 24. The conduit may be attached as by welding to the cylinder 24 without interfering with the movement of the piston plunger 25. A suitable end cap 65 is secured as by welding to one end of the oil cylinder 24, and suitable ports may be provided in the end cap leading to dashpot cushioning device 66, as will be explained hereafter. On the interior side of the end cap is formed a frusto-conical shaped plug 69 (FIG. 2) which is centered on the longitudinal axis of the accumulator. The plug 69 has an outer rounded shoulder wall 68 (FIG. which is adapted to be engaged by an internal, convexly cross sectioned annular wall 70 at the upper end of the plunger piston when the latter is at its upper limit position in the oil chamber 23. A cup-shaped opening 71 is formed within the facing end of the piston plunger 25 by the annular wall 70 and a circular plug 72 secured to an interior wall of the piston plunger. As the piston plunger moves to engage the plug 69, the oil within the opening 71 in the piston is squeezed through a diminishing space between the plug wall 68 and piston plunger wall 70 and into the cushioning device 66 to dampen the impact of the piston 25 abutting the end cap 65 at this limit position.

The preferred form of piston plunger 25 is an elongated cylindrically shaped tube which is substantially as long as either the gas cylinder 29 or the oil cylinder 24 so that one end of the piston plunger remains in engagement with the piston and guiding means 37 when the piston plunger is at its limit positions engaging and end caps 53 or 65. The piston is substantially hollow with a circular plug 72 adjacent the end which engages the end cap 65. The outer surface of the outer piston wall 39 is hardened and subsequently ground to have a substantially constant outer diameter dimension throughout its length.

The oil and gas cylinders 24 and 29 are secured together against an axially directed thrust exerted on their respective end caps 53 and 65 by a locking and coupling means 73. The preferred coupling means 73 includes lock pins 75 inserted into aligned apertures 77 in interleaved locking lugs 79 and 81 respectively which are secured to the gas and oil cylinders by locking rings 83 and 85 which are attached as by welding to the exterior wall of the respective oil and gas cylinders. More specifically the oil cylinder 24 has a locking ring 83 and welded thereto and on the outer circular surface of the locking ring are the series of radially projecting, integrally attached locking lugs 81. The longitudinally projecting lugs 79 for the gas cylinder 29 are integral with a lower ring 85 which is welded to a collar 86 fastened, as by welding, to an end of the gas cylinder 29. The respective locking lugs 79 and 81 are angularly related to be closely adjacent to one another and so that the apertures 77 may be aligned to receive the respective ones of the locking pins 75. Thus, with the locking pins fitted into the apertures in the lugs 79 and 81, the cylinders are held against separation from each other with application of opposing forces on the respective cylinder end caps 53 and 65.

The preferred form of guiding and sealing means 33 for the piston 25 is captured intermediate and held at the ends of the oil and gas cylinders 24 and 29 by the coupling means 73. The sleeve or bushing 35 of the guiding and sealing means is disposed between the adjacent ends of the cylinders and may be formed entirely from a bearing material such as brass or which may have separate bearing surfaces or inserts 87 and 89 of brass or babbit fitted therein. In either event the internal bearing surfaces 87 and 89 are suitably formed or machined to dimensions having a close tolerance, sliding fit with the outer diameter wall 39 of the piston plunger. These bearing surfaces 87 and 89 as will be appreciated, are quite small in longitudinal length as compared to the longitudinal extent of either one of the cylinder chambers; these bearing, by way of example, may be preferably formed of the relatively soft materials as compared to the hardened surface on the outer wall 39 of the piston plunger 25 so that dirt, metal chips or other foreign matter, which becomes inserted between the piston and the bearing surfaces, will embed in the softer bearing material without forming an elongated scratch or groove which will allow oil or gas to transfer across a bearing surface and/or seal. Also as explained, an annular groove 41 in the bushing 35 collects any air escaping the chamber 31 and this air is bled therefrom through the port 49 and line 47 to prevent air from moving into the oil chamber 23 and the possibility of dieselization. An indicator 90 such as a tell tale turbine in the line 47 measures and indicates the flow of air leaking so that the lost air may be replaced.

Suitable packings 91 and 93 having first, inner sides 94 resting on an outer ring wall of the bushing 35 assist in sealing against gas or oil leakage. Preferably, the packings 91 and 93 are U-cup in cross section although they may be of other shapes such as na O-ring or Chevron shaped ring. The U-cup packings have outwardly projecting legs 95 separated by an annular groove 96 and the legs 95 extend to abut inner bearings or ring seats 97 and 99 which are made of plastic material such as, for example, Teflon. These Teflon ring seats 97 and 99 are preferably split rings having a gap therein of about 1/2 inch so that oil and gas may flow to opposite sides thereof and thereby prevent the gas or oil from exerting pressure in the longitudinal direction as would in turn exert mechanical pressure on the packing legs 95. The split ring also facilitates insertion and assembly of the ring seats 97 and 99. The ring seats may also be provided with a radially projecting shoulder 100 for seating in a groove in the respective cylinder walls to hold the ring seats against movement in the longitudinal direction as would exert mechanical pressure on the packing legs 95.

The Teflon ring seat 97 is inserted into an enlarged bore 98 formed in the wall of the oil cylinder 24 to abut an annular shoulder 101. The teflon ring 99 for the packing 93 rests on a shoulder 105 of the collar 86 which is welded to the top of the gas cylinder wall. A circular, longitudinally extending wall 107 of the collar 86 encircles the ring seat 99 and packing 93 and a portion of the bushing 35 to hold each of them in place for engagement with the piston wall 39.

At the oil cylinder 24, a reduced cross-sectioned end wall 108 encircles the ring seat 97, packing 91 and a portion of the bushing 35 to hold them in place for engagement with the piston wall 39. When the locking pins 75 are inserted into the respective apertures 77 in the locking lugs 79 and 81, respective packings 91 and 93 are held in sealing engagement with the exterior wall 39 of the piston plunger 25 and they remain in engagement therewith due to the long length of the piston plunger.

The position of the piston plunger 25 in the accumulator housing 22 may be advantageously sensed for control of the hydraulic apparatus by means which extends into the annular space 52 between the piston plunger 25 and the cylindrical bore wall 51 and provides a suitable electrical read out such as, for example, signals when the piston plunger approaches and reaches either one of its limit positions. More specifically, first and second sets of transducers 112 and 113 may be positioned adjacent the end cap 53 with the upper set of transducers sensing the approach of the piston toward the end wall and the other set of transducers 113 sensing the presence or absence of the piston end. Preferably, the transducers are sound transducers and each set of transducers includes a pair of transducers which are located circumferentially at 180 from each other and at the same longitudinal distance from the end cap 53. In a similar manner, sets of opposed transducers 114 and 115 may be provided at the upper end of the cylinder to sense first the approach and then the arrival of the piston plunger at the other limit position in which the top end of the piston plunger engages the plug 69 on the end cap 65.

For some installations, it may be more desirable to have the accumulator 11 positioned generally horizontally rather than in an upright position as illustrated. When the accumulator is disposed vertically the piston plunger 25 does not require guiding other than that provided by the bearing surfaces 87 and 89. However, when the accumulator is disposed horizontally, the elongated piston 25 is suitably supported for sliding movement by shoes 117 (FIG. 4) inserted in the annular clearance space 52 and having arcuate supporting faces 119 of the suitable bearing material. Preferably the shoes are disposed on the lower side of the gas cylinder 29 and are spaced angularly from each other and upwardly along the cylinder wall 51 from the bottom of the cylinder to provide a cavity therebetween into which dirt or other foreign matter tends to settle by gravity at the bottom of the cylinder rather than settling on arcuate bearing faces 1 19. It will, of course, be realized that such shoes may be disposed at places other than those places described or illustrated and may also be used in the oil cylinder 24 if so desired.

The ability to use compressed air rather than nitrogen as the gas in the chamber 31 provides a number of significant advantages and greater flexibility for using the hydraulic apparatus. For example, the

compressed air precharge of the gas chamber 31 or the replenishing of lost air therefrom may be obtained from a simple system, such as illustrated in FIG. 1, in which an electric motor 121 drives an air compressor 123 which maintains a quanity of air in a receiver tank 125 which is suitably connected to the gas cylinder 29. A compressed air system usually requires less storage space than a large number of interconnected nitrogen filled bottles. Also, the nitrogen bottles are no longer effective once the pressure has been considerably reduced, and then it is usually necessary to return the nitrogen bottles to a supplier. The nitrogen gas within the bottles, of course, is not all expended. With the compressed air system, the pressure within the cylinder 29 and the energy stored and released from the accumulator 11 to the machine 13 may be easily varied or adjusted to a higher or a lower pressure by varying the precharge pressure of air in the gas chamber 31. To allow adjustment to a lower pressure, a bleed line 127 is connected through a suitable valve 129 to a supply line 131 leading to the port 55 for the cylinder 29. To reduce pressure within the gas chamber, the bleed valve is opened while a valve 142 leading to the receiver 125 is closed. A suitable pressure gauge 134 may be connected to the supply line 131 to indicate the pressure in the system to assist in monitoring or establishing a higher or lower air pressure for the gas cylinder 29.

To provide the capability of automatically monitoring and maintaining a predetermined gas pressure in the gas cylinder 29, a pressure sensitive switch 141 may be connected to the pressure gauge 134 for monitoring the pressure in the supply line 131 and within the gas chamber 31. When the gas pressure falls below a predetermined level, the pressure switch 141 will operate the circuit solenoid controlled valve 142 to release compressed air from the receiver 125 to raise the air pressure in the cylinder chamber to the predetermined level at which time the pressure sensitive switch will cause the solenoid to close the valve 142.

Also, any oil lost by leaking from the system may be replaced by operation of an oil pump 147 (FIG. 1) which is connected to an oil reservoir to force oil through a one way check valve 149 and line 151 back into line 21 leading to the oil chamber 23.

In this illustrated embodiment of the invention, the piston plunger 25 is normally seated on the end cap 53 when in the at-rest limit position. A hydraulic operation may be commenced by opening a normally closed valve 153, (FIG. 1) in the conduit 21. The oil in the press cylinder 14 is at a pressure which is substantially less than the pressure in the accumulator oil cylinder 24 so that opening of the control valve establishes a pressure difierential sufficient that oil flows through the conduit 21 and into the press cylinder 14. The unseating of the ram 15 and its movement away from its seat maintains a pressure differential to cause oil to continue to flow into the press cylinder. Oil flowing from the oil chamber 23 causes a reduced pressure therein relative to the pressure in the gas chamber. Thus, the piston plunger 25 will unseat and continue to rise, as viewed in these FIGURES. When the piston plunger is about to reach the upper limit position, the set of transducers 114 sense the passage of the lower end of the piston plunger and cause an electrical control circuit means to begin closing the valve 153 or otherwise throttling the flow of oil to the press cylinder 14. Then, when the piston plunger is in a position which is higher than the position sensed by the transducer 114, the transducers 115 may produce a read out to stop the flow of oil to the press cylinder 14 by closing the control valve 153.

At this time the dampening device 66 is cushioning and dampening the impact of the piston plunger 25 on the end cap plug 69. More specifically, a small restricted orifice in a passageway or bore 157 in the end cap plug 69 provides fluid communicate between oil chamber 23 and an oil receiver tank 159 on the outside the accumulator housing. A suitable valve means such as a check valve 161 allows flow of oil through the passageway 157 but blocks any return flow of oil from the cushioning device through the passageway 157. Another return passageway 158 is provided in the end plug 65 and a valve 163 blocks return flow of oil through the passageway 158 from the dampening device 66 to oil chamber 23 until the valve 163 is open, either manually or by a solenoid.

For the purpose of returning the piston plunger 25 and ram 15 to their at rest positions, an oil pump 165 is operated to begin pumping oil from a first line 167 leading to the conduit 21 and press cylinder 14 to a return line 169 which by passes the control valve 153 and check valve 155 in the conduit 21 The pump will continue to pump oil to the oil cylinder chamber 23 and to raise the pressure therein to a pressure greater than the pressure in gas chamber 31. As the plug 69 is not fully telescoped into the piston opening 71 and there is sufficient area available at the top of piston plunger for the higher pressure oil in the oil chamber to press on the upper end of the piston plunger and force the same down against the lower pressure gas in the gas chamber'31. At this or a later time, the valve 163 for the cushioning device 66 may be opened to allow oil to return therefrom through the passageway 158 to the oil chamber. As the piston plunger approaches the end cap 53, the set of transducers 112 will sense the lower end of the piston plunger and operate controls to slow down the pump 165 and thereby the oil flow rate so that the piston plunger will decelerate. The lower set of transducers 113 may be used to sense the return of the lower end of the piston plunger 25 and to turn off the oil pump 165 at which time the press ram 15 should also be returned to its non-working position.

The fluid power released from the accumulator may be varied by varying not only the pressure of the precharge gas, as above explained, but also by varying the volume of the precharge gas. If it is desired to reduce the rate of change of the pressure drop occuring as a result of the piston plunger 25 moving to its upper limit position, a series of connected compressed air bottles or a tank 171 may be attached by a line 173 to a port in the side wall of the gas cylinder so that a larger initial precharge gas volume is available. It will be appreciated that change in volume will about equal to the volume of the inner gas receiving bore of the piston plunger 25 and the volume occupied by the cylindrical piston plunger wall. Also, having the piston plunger 25 hollow and filled with compressed gas provides additional volume over the usual solid or closed kind of piston used in the prior art. Preferably, a valve 175 is provided in the line 173 so that the extra volume of the tank 171 may be added or subtracted to achieve different pressure drop characteristics. For example, with the valve 175 open and the tank 171 in fluid communication with the gas chamber, the pressure drop experienced with movement of the piston plunger from its limit position at end cap 53 to end cap 65 may be plotted as curve 177 on graph 178, as illustrated in FIG. 6. On the other hand, if the valve 175 is closed and the piston plunger is again shifted upwardly to its upper limit position, the pressure in gas chamber may drop more quickly along curve 179 due to the greater increase in volume change occuring.

If it is desired to achieve a greater pressure drop, this may be achieved by decreasing the precharge volume for the gas such as by adding a liquid, e.g. water, into the gas cylinder 29 to decrease the initial volume in the chamber 31 available for gas. Thus, with a movement of the piston plunger to its upper limit position, the percentage of volume change is increased, as the gas is free to expand to provide a greater pressure drop as for example along curve 181. As stated previously, the initial precharge pressure may be readily raised by operating the compressor system, or alternatively the initial precharge pressure may be lowered by opening bleed line valve 129. Similar operating curves at a lower pressure and with a large volume and with a lesser volume are indicated by curves 183 and 185, respectively in FIG. 6. Thus, there is provided a very simple and effective control of the fluid power stored and released from the accumulator to the hydraulic apparatus 13 by merely varying the pressure and/or volume of the precharge gas in the accumulator.

As an aid to understanding the invention, a brief description of the operation of the accumulator 11 in connection with a hydraulic press 13 will now be given. With the press ram 15 seated at the base of the cylinder, and with control valve 153 in the conduit 21 closed, the piston plunger 25 will be seated on end cap 53 awaiting opening of this valve. By opening the control valve 153 oil which is greater pressure in the oil chamber 23 than in the press cylinder 14, flows through the conduit 21 and to the press ram 15 and exerts suffrcient pressure and force on the entire surface of the ram, which is exposed to the oil pressure, to cause the ram to move forwardly. As the ram accelerates, it allows more oil to flow through the conduit 21. The oil flowing from the oil chamber 23 causes the pressure therein to drop below the gas pressure in the gas chamber 31. Therefore, the higher pressure gas forces the piston plunger 25 from its lower limit position and its exterior piston wall 39 slides along the bearing surfaces 87 and 89 of the bushing 35 and these bearing surfaces together with the packing 93 maintain a complete separation of the gas from the oil. Hence, compressed air rather than nitrogen may be used as the gas within the gas chamber 31. Should any air leak past the packing 93 and bearing surface 89 it will be bled from the groove 49 and bleed line 47. The air indicator will indicate the amount of air flow loss, if any.

As the piston completes its forward travel toward the upper limit position, the transducers 114 will sense the passing of the lower end of the piston plunger 25 and cause the control valve 153 to move to a position to restrict flow of oil through the conduit 21 and when the lower end of the piston plunger passes the transducers 115 the control valve is closed and stops oil flow into the press cylinder 14. During this terminal movement of the piston plunger 25, oil is forced through a small restrictive orifice in the passageway 157 and into the cushioning device 66. As opening 71 in the piston plunger approaches the plug 69, the curved wall 70 of piston plunger moves toward a position to abut the rounded corner 68 on the plug 69 to limit further upward travel while preventing the piston plunger from binding on the plug.

The piston plunger 25 and the ram may be returned in various manners such as by suitable valves and fluid controlled thereby; but, in this instance, the return pump 165 is started and pumps oil from the press cylinder 14 through by-pass lines 167 and 169 about the now closed control valve 153 and check valve 155 into the oil chamber 23. As there is an annular ring of liquid about the sides of the piston plunger above the top of piston plunger, the increased pressure caused by the oil flowing into. the oil chamber 23 will establish a pressure differential with the gas in chamber 31 sufficient to unseat the piston plunger and force it down. When the lower end of piston plunger is sensed by the transducers 112, the pump 165 may be controlled to provide a restricted flow of oil so that piston plunger will decelerate. When the lower end of the piston plunger is sensed by the transducers 113, the pump 165 may be shut off to stop the flow of oil from the press cylinder 14 to the accumulator oil cylinder.

From the foregoing, it will be seen that the accumulator may be constructed with a housing including a pair of joined cylinders each having unmachined inter nal bores with a piston having an outer wall machined to accurate size to seal with bearing surface means. The bearing surfaces may be short in length in comparison to the length of the cylinders and to the length of the piston. By using soft bearing material in the piston guiding and sealing means, dirt of other foreign material, which would scratch machined internal cylinder walls, becomes embedded in the bearing material and less prone to cause leakage. Should leakage occur, the annular groove and port will discharge the leaking material. As the preferred accumulator construction is suitable for use with a compressed air system rather than nitrogen, it is less expensive, less bulky and provides more flexibility in operating pressure, volume and power than are conventional, nitrogen using systems.

The accumulator is particularly adapted for use in corrosive applications in which the cylinder bore and/or piston plunger is subject to pitting kinds of corrosion. In corrosive applications, a visual maintenance inspection of long internal, machined bore surface within a cylinder for small pits is a difficult and time consuming operation whereas the visual inspection of the cylindrical surface of the piston plunger is quite eas While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A piston accumulator for delivering bursts of hydraulic energy to a high velocity hydraulic press, said accumulator comprising a housing means providing a liquid receiving chamber and a gas receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and gas chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and gas chambers being spaced from said outer cylindrical wall of said piston plunger, piston plunger guiding and sealing means intermediate said liquid and gas chambers and including a gas seal means to prevent the transfer of gas into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said gas chamber, said piston plunger and guiding means having a bearing surface of a material which is substantially softer than the outer cylindrical wall of said piston plunger so that dirt will embed in said bearing material before scoring said outer cylindrical wall, means including a port for said liquid seal and said gas seal means to discharge gas or liquid leaking past one of said seal means, and means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, said means to smoothly arrest said piston plunger including a dashpot means acted upon by liquid in said liquid chamber and further including transducer means to sense the position of said piston plunger during its travel and means operable by said transducer means to reduce the fore being applied to the piston plunger.

2. An accumulator in accordance with claim 1 in which said housing means is disposed substantially horizon-tally, said piston plunger is disposed substantially horizontally for travel along a substantially horizontal path, and in which support shoes having bearing surfaces thereon project from said side wall of said gas chamber to engage the piston plunger and to support the same at positions spaced longitudinally in said gas chamber from said piston guiding and sealing means, said support shoes being spaced circumferentially from the lowermost portion of said side wall of said gas chamber.

3. An accumulator in accordance with claim 1 in which said dashpot means includes a restricted orifice and an elongated passageway through which liquid from said liquid chamber may be forced to flow during the terminal portion of the piston plungers travel in one direction.

4. An accumulator in accordance with claim 1 in which said means including a port further comprises an annular groove formed in said housing means and positioned intermediate said gas seal means and said liquid seal means and in fluid communication with said port and a monitoring and indicating means to monitor and to indicate the amount of leakage through said port from said housing means.

5. A piston accumulator for delivering bursts of hydraulic energy to a high velocity hydraulic press, said accumulator comprising a housing means providing a liquid receiving chamber and a gas receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and gas chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and gas chambers being spaced from said outer cylindrical wall of said piston plunger, piston plunger guiding and sealing means intermediate said gas chambers and including a gas seal means to prevent the transfer of gas into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said gas chamber, said piston plunger and guiding means having a bearing surface of a material which is substantially softer than the outer cylindrical wall of said piston plunger so that dirt will embed in said bearing material before scoring said outer cylindrical wall, means including a port for said liquid seal and said gas seal means to discharge gas or liquid leaking past one of said seal means, and means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, said means to smoothly arrest said piston plunger including a dashpot means acted upon by liquid in said liquid chamber and further including sound transducers inserted into said wall of housing means to detect the position of said piston plunger during its travel.

6. An accumulator in accordance with claim in which said sound transducers are positioned adjacent opposite ends of said gas chamber to sense the position of the piston plunger adjacent either limit position in its travel.

7. A piston accumulator for imparting a burst of hydraulic energy to a hydraulic machine comprising a housing means providing a liquid receiving chamber and an air receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and air chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and said air chambers being spaced from said outer wall of said piston plunger, piston guiding and sealing means intermediate said liquid and air chambers and including an air seal means to prevent the transfer of air into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said air chamber, means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic machine and said piston accumulator, means connected in fluid communication with said air chamber for varying the precharge volume of pressure air for said air chamber and thereby varying the rate of pressure drop ex perienced with movement of said piston plunger, and means connected to said air chamber for varying the pressure of air in said air chamber to enable a change to be made in the kinetic energy and the hydraulic energy imparted to said hydraulic machine by said piston plunger.

8. A piston accumulator in accordance with claim 7 in which an air inlet port is provided at the bottom of said air receiving chamber to collect leaking liquid therein and a venting means is connected to said air inlet port to vent air and liquid collected at said air inlet port from said air receiving chamber.

9. A piston accumulator in accordance with claim 7 in which said means to smoothly arrest said piston plunger further comprises a dashpot means acted upon by liquid in said liquid chamber.

10. A piston accumulator in accordance with claim 9 in which said dashpot means comprises a cooperating 253F532? fiofiisiil lfiilif fifififeh fiifi 'if cavity to squeeze liquid therefrom when said piston plunger is being arrested.

11. A combination of a piston accumulator and a high velocity hydraulic press, said combination comprising a cylinder in said press, a piston in said press cylinder for receiving a burst of hydraulic energy from liquid under pressure in said piston accumulator, an accumulator housing means providing a liquid chamber and an air receiving chamber, passageway means between said press cylinder and said liquid chamber, an elongated piston plunger within said accumulator housing means and movable by a difierential pressure between and within said liquid and air chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and said air chambers being spaced from said outer wall of said piston plunger, piston plunger guiding and sealing means intermediate said liquid and air chambers and including an air seal means to prevent the transfer of air into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said air chamber, means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, means for varying the precharge volume of air for said air chamber to change rate of pressure drop of air in said air cylinder being experienced with movement of said piston plunger, and means for varying the pressure of air in said air chamber to enable a change in kinetic energy and the hydraulic energy imparted by said liquid under pressure to said piston in said press cylinder. 

1. A piston accumulator for delivering bursts of hydraulic energy to a high velocity hydraulic press, said accumulator comprising a housing means providing a liquid receiving chamber and a gas receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and gas chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and gas chambers being spaced from said outer cylindrical wall of said piston plunger, piston plunger guiding and sealing means intermediate said liquid and gas chambers and including a gas seal means to prevent the transfer of gas into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said gas chamber, said piston plunger and guiding means having a bearing surface of a material which is substantially softer than the outer cylindrical wall of said piston plunger so that dirt will embed in said bearing material before scoring said outer cylindrical wall, means including a port for said liquid seal and said gas seal means to discharge gas or liquid leaking past one of said seal means, and means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, said means to smoothly arrest said piston plunger including a dashpot means acted upon by liquid in said liquid chamber and further including transducer means to sense the position of said piston plunger during its travel and means operable by said transducer means to reduce the fore being applied to the piston plunger.
 2. An accumulator in accordance with claim 1 in which said housing means is disposed substantially horizon-tally, said piston plunger is disposed substantially horizontally for travel along a substantially horizontal path, and in which support shoes having bearing surfaces thereon project from said side wall of said gas chamber to engage the piston plunger and to support the same at positions spaced longitudinally in said gas chamber from said piston guiding and sealing means, said support shoes being spaced circumferentially from the lowermost portion of said side wall of said gas chamber.
 3. An accumulator in accordance with claim 1 in which said dashpot means includes a restricted orifice and an elongated passageway through which liquid from said liquid chamber may be forced to flow during the terminal portion of the piston plunger''s travel in one direction.
 4. An accumulator in accordance with claim 1 in which said means including a port further comprises an annular groove formed in said housing means and positioned intermediate said gas seal and said liquid seal and in fluid communication with said port and a monitoring and indicating means to monitor and to indicate the amount of leakage through said port from said housing means.
 5. A piston accumulator for delivering bursts of hydraulic energy to a high velocity hydraulic press, said accumulator comprising a housing means providing a liquid receiving chamber and a gas receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and gas chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and gas chambers being spaced from said outer cylindrical wall of said piston plunger, piston plunger guiding and sealing means intermediate said gas chambers and including a gas seal means to prevent the transfer of gas into said liquid chamber and a liquid seal meAns to prevent the transfer of liquid into said gas chamber, said piston plunger and guiding means having a bearing surface of a material which is substantially softer than the outer cylindrical wall of said piston plunger so that dirt will embed in said bearing material before scoring said outer cylindrical wall, means including a port for said liquid seal and said gas seal means to discharge gas or liquid leaking past one of said seal means, and means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, said means to smoothly arrest said piston plunger including a dashpot means acted upon by liquid in said liquid chamber and further including sound transducers inserted into said wall of housing means to detect the position of said piston plunger during its travel.
 6. An accumulator in accordance with claim 5 in which said sound transducers are positioned adjacent opposite ends of said gas chamber to sense the position of the piston plunger adjacent either limit position in its travel.
 7. A piston accumulator for imparting a burst of hydraulic energy to a hydraulic machine comprising a housing means providing a liquid receiving chamber and an air receiving chamber, an elongated piston plunger within said housing means and movable by a differential pressure between and within said liquid and air chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and said air chambers being spaced from said outer wall of said piston plunger, piston guiding and sealing means intermediate said liquid and air chambers and including an air seal means to prevent the transfer of air into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said air chamber, means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic machine and said piston accumulator, means connected in fluid communication with said air chamber for varying the precharge volume of pressure air for said air chamber and thereby varying the rate of pressure drop experienced with movement of said piston plunger, and means connected to said air chamber for varying the pressure of air in said air chamber to enable a change to be made in the kinetic energy and the hydraulic energy imparted to said hydraulic machine by said piston plunger.
 8. A piston accumulator in accordance with claim 7 in which an air inlet port is provided at the bottom of said air receiving chamber to collect leaking liquid therein and a venting means is connected to said air inlet port to vent air and liquid collected at said air inlet port from said air receiving chamber.
 9. A piston accumulator in accordance with claim 7 in which said means to smoothly arrest said piston plunger further comprises a dashpot means acted upon by liquid in said liquid chamber.
 10. A piston accumulator in accordance with claim 9 in which said dashpot means comprises a cooperating plug and a plug receiving cavity on said piston plunger and said housing means, said plug projecting into said cavity to squeeze liquid therefrom when said piston plunger is being arrested.
 11. A combination of a piston accumulator and a high velocity hydraulic press, said combination comprising a cylinder in said press, a piston in said press cylinder for receiving a burst of hydraulic energy from liquid under pressure in said piston accumulator, an accumulator housing means providing a liquid chamber and an air receiving chamber, passageway means between said press cylinder and said liquid chamber, an elongated piston plunger within said accumulator housing means and movable by a differential pressure between and within said liquid and air chambers, said piston plunger having an outer cylindrical wall, side walls in said liquid and said air chambers being spaced from said outer wall of said piston plunger, piston plunger guiding and sealing means intermediate said liquid and air chambeRs and including an air seal means to prevent the transfer of air into said liquid chamber and a liquid seal means to prevent the transfer of liquid into said air chamber, means to smoothly arrest said piston plunger without excessive hydraulic and mechanical shock to said hydraulic press and said piston accumulator, means for varying the precharge volume of air for said air chamber to change rate of pressure drop of air in said air cylinder being experienced with movement of said piston plunger, and means for varying the pressure of air in said air chamber to enable a change in kinetic energy and the hydraulic energy imparted by said liquid under pressure to said piston in said press cylinder. 